1. First author: Department of Plant Pathology and Environmental Microbiology, Center for Infectious Disease Dynamics, Pennsylvania State University, University Park, PA 16802; second author: Computational Biology Group, Institute of Infectious Diseases and Molecular Medicine, University of Cape Town, Cape Town, 7925 South Africa; and third author: CIRAD, UMR BGPI, Campus International de Montferrier-Baillarguet, 34398 Montpellier Cedex-5, France.